Simultaneous Nitrification/Denitrification in an Integrated Fixed-Film Activated Under a Limited Filamentous Bulking State

Simultaneous nitrification and denitrification (SND) in one reactor has been realized with different methods in previous research. In this study, porous polymer biofilm carriers together with suspended biomass were fluidized in an airlift membrane bioreactor reactor. Limited filamentous bulking (LFB) was used to enhance SND, synthetic wastewater with mean ammonium-nitrogen concentrations of 50 mg/L was treated in the system, achieving 70% nitrogen removal. Batch experiments clearly demonstrated that nitrification was localized in the suspended biomass and attached on the carriers, while denitrification was confined within the bioparticles of the slowly degrading biocompounds. High-throughput sequencing analyses confirmed that heterotrophic nitrifying bacteria were the nitrogen-transforming functional bacteria in both the sludge and biofilm of the integrated fixed-film activated system, with Rhodobacter being the dominant genus. The LFB state-causing agent was identified as Thiothrix , which was present in the integrated fixed-film activated.